Dehydroalkylation process



United States Patent Ofiice 2,759,027 Patented Aug. 14, 1956 DEHYDRoALrorLArroN rnocass Joe T. Kelly, Galveston, Francis T. Wadsworth, Dicln'nson, and Robert J. Lee, LaMarque, Tex., assignors to The American Oil Company N Drawing. Application May 27, 1954, Serial No. 432,892

6 Claims. c1. 260-671) This invention relates to the preparation of tertiary alkylbenzenes by the alkylation of a benzene-type hydrocarbon with an isoparafiin. More particularly, the invention relates to the preparation of tertiary butylbenzenes by dehydroalkylation process utilizing a branched chain olefin as the hydrogen acceptor.

It is known that tertiary alkylbenzenes, such as tbutylbenzene or t-butyltoluene, can be prepared by the reaction of an aromatic hydrocarbon with an isoparaffin in the presence of an olefin hydrogen acceptor; the catalyst utilized is an acidic-type catalyst such as is used for the alkylation of isobutane with an olefin. However, the yield of tertiary alkylbenzene is low when operating with the prior art propylene or n-butylene olefin hydrogen acceptor. An object of the invention is a dehydroalkylation process for the preparation of tertiary alkylbenzenes in greater yield than in the conventional process. Another object of the invention is the preparation of para-ditertiary butylbenzene by the reaction of benzene and isobutane in the presence of an acidic type alkylation catalyst. Still another object is the preparation of paratertiary butyltoluene by the reaction of toluene and isobutane in the presence of an acidic type alkylation catalyst. A particular object of the invention is a process for the preparation of tertiary alkylbenzenes by a process which does not require a high purity olefin. Other objects of the invention will become apparent in the course of the detailed description thereof.

The process of this invention involves the reaction of an aromatic hydrocarbon selected from the class consisting of benzene, toluene, xylene, and ethylbenzene and an isoparafiin containing from 4 to 12 carbon atoms in the presence of a branched chain olefin hydrogen acceptor, containing from 4 to 12 carbon atoms and having a configuration difierent fiom that of the isoparaffin. The reaction is carried out in the presence of a sulfuric acid alkylation catalyst and at a temperature between about 0 C. and about 30 C. The isoparafiin and the defined aromatic hydrocarbon are present in a molar ratio of at least about 3. The branched chain olefin is present in an amount about equal to the amount of isoparafiin reacting with the aromatic hydrocarbon. When the aromatic hydrocarbon is benzene, the molar ratio of branched chain olefin to benzene is about 2; and when the aromatic hydrocarbon is other than benzene, the molar ratio of branched chain olefin to aromatic hydrocarbon is about 1. The aromatic hydrocarbon and the isoparatlin react to produce an aromatic hydrocarbon alkylate with a tertiary alkyl group and the branched chain olefin is converted to a paraflin.

The aromatic hydrocarbon charged to the process of this invention is selected from the class consisting of benzene, toluene, xylene, and ethylbenzene. Mixtures of these may be used. Also, the aromatic hydrocarbons may be introduced in the form of a natural mixture of aromatic hydrocarbons and non-aromatic hydrocarbons; for example, a petroleum naphtha boiling closely about the boiling point of benzene or toluene.

The isoparaflin charged to the process is one containing from 4 to 12 carbon atoms. Examples of suitable isoparafiins are: 2-methylpropane (isobutane), Z-methylbutane (isopentane), 2-methylpentane, 3-methlypentane, 2-methylhexane, 3-methylhexane, 3-ethylpentane, 2- methylheptane, 3-ethylhexane, 2,2,3-trimethylpentane, 2- methyloctane, 3-methy1octane, Z-methylnonane, Z-methyldecane and 2-ethyldecane. The preferred isoparafiins are isobutane and isopentane.

The yield of tertiary alkylbenzene is vastly improved when the hydrogen acceptor is an iso-olefin rather than a normal olefin. The branched chain olefins used in this process contain from 4 to 12 carbon atoms and have a configuration different from that of the particular isoparafiin used. The word configuration is used herein as synonymous with the skeletal structure of the isoparafiin. To illustrate: isobutane and isobutene have the same configuration or skeletal structure. Examples of the branched chain olefins which may be utilized in the process are: Z-methylpropene, Z-methylbutene-l, 3- methylbutene-l, 2-methylbutene-2, Z-methylpentene-l, 3- methylpentene-l, 4-methylpentene-1, Z-methylpentene-Z, 3-methylpentene-2, Z-ethyIbutene-l, 2-methlyhexene-1, 2- methylhexene-Z, 3-ethylpentene-2, 3-methylheptene-l, 2,4,4-trimethylpentene-l, 3,3,4-trimethylpentene-l, 2,4,4- trimethylpentene 2, 2,3 dimethylheptene 2, 3 ethylheptene-3, 3-ethyloctene-2, and 3,5,5-trimethylheptene-3. It is preferred to utilize a branched chain olefin wherein the double bond is positioned very close to a tertiary hydrogen atom and wherein no quaternary arrangement is present. Examples of the preferred branched chainolefins are: 2 methylbutene 2, 2 methylpentene 2, 3 methylpentene-2, 2-methylheXene-l, Z-methylhexene-Z, 2- methylheptene 2, 2,3,4 trimethylpentene 2, 2,5,5 trimethylhexene-Z.

In addition to the single compounds set out above, the process may utilize mixtures of branched chain olefins, particularly mixtures which are readily available in ordinary refinery operations. The gasoline boiling range material derived from the polymerization of propylene and butlyenes is particularly suitable for use in this process. It is understood that the propylene polymer, butylene polymer or propylene-butylene co-polyrner utilized contains not more than 12 carbon atoms. By utilizing these polymers, it is possible to obtain a high octane number material of great value for use in gasoline at very little cost.

Competing reactions are involved in the process of this invention. Thus, it is possible that the olefins and the isoparafiin will alkylate the aromatic hydrocarbon. However, the olefin alkylation can be suppressed almost entirely by utilizing a large amount of the isoparaffin relative to the olefin present and also operating with a branched chain olefin. The molar ratio of isoparaffin to aromatic hydrocarbon in the alkylation zone is at least about 3. A larger ratio is helpful in suppressing side reactions and it is preferred to operate with a ratio of at least about 10.

The branched chain olefin determines the yield of t-alkylbenzene product up to the point at which all the aromatic hydrocarbon has been alkylated. In order to maximize the yield of aromatic hydrocarbon alkylated, the molar ratio of branched chain olefin to aromatic hydrocarbon is the same as the amount of isoparaiiin alkylation that takes place. The alkylate from the reaction of benzene and isoparafiin is almost entirely the di-t alkyh benzene. Therefore, the moi ratio of branched chain olefin to benzene is about 2. When toluene, xylene, or ethylbenzene are the feed aromatics, the alkylate contains essentially only one t-alkyl group; therefore, when using these aromatics as the charge, the molar ratio of branched chain olefin to aromatic hydrocarbon is about 1. The

use of amounts of olefins in excess of these amounts is undesirable since the excess olefin appears to participate in an alkylation reaction with the isoparafiin and aromatic to give high boiling material. 7

The alkylation is carried out in the resence of a sub furic acid alkylation catalyst, that is, the type of sulfuric acid catalyst utilized in the conventional alkylation of isobutane and butene. The sulfuric acid concentration is generally between about 85% and 100%. It is preferred to operate the process of this invention with sulfuric acid having a concentration between about 88 and 92%. The acid utilized here may be fresh acid made from sulfur or recovered acid from other refinery operations. Particularly good results are obtained when spent acid from the alkylation of isobutane and butenes is used as the catalyst in the process of this invention.

In general, the amount of catalyst used may be about the amounts used in conventional isobutane-butene alkylation. Herein, the volume ratio of acid to total hydrocarbon present in the alkylation zone is between about 0.5 and about 2; preferably, the acid to hydrocarbon ratio is between about 1 and about 1.5. The term total hydrocarbon is intended to mean the sum of the aromatic hydrocarbon, the isoparafiin, branched chain olefin and any inert hydrocarbons which may also be present in the alkylation zone.

In general, the dehydroalkylation reaction may be carried out at about the same temperatures as conventional sulfuric acid alkylation of isobutane and butenes. In general, the temperature used herein is between about C. and about 50 C. Preferably the temperature of the alkylation zone is maintained between about and 15 C.

The reactants and the catalyst are held in the alkylation zone for a period of time suificient to substantially complete the dehydroalkylation reaction. This time will vary with the type of reactants charged, the cata lyst concentration, the catalyst-hydrocarbon ratio, and the temperature of operation. in general, the reaction time is between about 5 minutes and about 60 minutes. Under the preferred conditions of operation, the reaction time is between about 20 minutes and 40 minutes.

The results obtainable with the process of this inventionare illustrated by the following examples, which examples do not limit the scope of the invention.

The reaction was studied under flow conditions. The equipment consisted essentially of a lO-gallon weigh tank for charge, a 1.2l-gallon capacity reactor, a settler, and a lO-gallon weigh tank as product receiver. The reactor was equipped with mechanical stirrer, internal bafiies, and cooling jacket.

The operating procedure was as follows: The isobutane, olefin and aromatic charge mixture were prebl-ended in the charge tank. The catalyst (2590 ml.) was charged to the reactor and the reactor cooled to operating temperature of (It-30 C. by circulation of coolant through the jacket. The volume ratio of catalyst to total hydrocarbon charged was, in all the tests, close to 1.3. in all cases the 90% acid was a spent alkylation catalyst; the other acids were fresh acids. The reaction system was pressured with nitrogen to an operating pressure of about 60 p. s. i.,g., which pressure was sutlicient to maintain the reactants in the liquid phase throughout the system. The liquid hydrocarbon was pressured from the charge vessel, through a flowrator, a manual control valve, and into the reactor. The reactor efiluent passed to the settler, where the catalyst was separated and returned by gravity to the reactor, while the product passed on to the product receiver. Reaction pressure was maintained by manually bleeding gaseous product from the receiver through a gas meter and sampler.

In test No. 16, the catalyst utilized was 8P3 hydrate containing 75% of BFs. The volume ratio of catalyst to hydrocarbon in this test was 1.3.

The isobutane utilized in these tests was derived from 1 properties and infrared measurements. The aromatic from 4 to 6 carbon atoms.

' was isobutane.

hydrocarbons used were nitration grade.

The reaction product mixture was distilled to remove the unreacted isobutane and n-butane. A narrow boiling cut corresponding to the t-alkylbenzene was then analyzed by infrared technique for the presence of di-tbutylbenzene or t-butyltoluene. The infrared analysis was sufiiciently accurate to permit the determination of the distribution of the para and meta isomers. In all of the tests utilizing benzene, only trace amount of meta-dit-butylbenzene was found to be present. In the case of some of the tests, the liquid product was fractionated to produce a cut boiling closely about the boiling point of di-t-butylbenzene. By crystallization methods the dit-butylbenzene was recovered from this cut. In the tabulation of the results, the yield of di-t-butylbenzene is given, where possible, on both the infrared determination and also the actual recovery determination. Where enough olefin was not present to permit the alkylation of all the aromatic hydrocarbon, the yield of t-alkyl alkylate was set up on the basis of the theoretically possible alkylation product; this, in order to avoid giving a false impression of unusually low yield.

Tests 1-9 are set out in Table .I. In these tests, the aromatic hydrocarbon was benzene and the isoparatfin Test No. 1 was carried out to determine the amount of alkylation obtainable in the absence of an olefin-hydrogen acceptor. No product was obtained. Tests 2-4 were carried out with normal olefins having These tests show that the maximum yield of di-t-butylbenzene was only 59% and this when using peritenc-Z as the olefin. Tests 5 through 8 were carried out using branched chain olefins. In all of these tests, the yield of para-di-t-butylbenzene, on a recovered basis, was more than double that of the highest yield when using an n-olefin. Test No; 8 provides a comparison between the actual recovery yield and the infrared yield when high conversion is being obtained.

Test No. 5 utilizing the 5 carbon atom, Z-methylbutene-l,

yield of di-t-butylbenzene is much greater than the infrared yield of test No. 8. These tests show the favorableinfluence of having the double bond close to the tertiary hydrogen atom.

Test No. 7 shows that very high yield of alkylate is obtainable when using a highly branched octane. as the acceptor. The yield obtained in test No. 7 is within experimental error, identical to that obtained in test No. 5 wherein a 5 carbon atom branched olefin was used. This result was in marked contrast to the results oftests 3-4 wherein the 6 carbon atom n-olefin gave a much lower yield than the 5 carbon atom n-olefin.

In Table H are set out the results using toluene as the aromatic hydrocarbon. Inthese tests, the infrared analy sis showed the presence of at least trace amounts of the' TABLE I Results using benzene and isobutane Test No 1 2 3 4 5 6 7 8 9 2-rnethyl- 4-methyl- 2,4,4- tri- 4-methyl- 4-methyl- Olefin None Butene-l Pentene-Z Hexene-l butene-l pentene-2 methylpentene-l pentene-1 pentene-2 H1504 conc. 9O 90 90 99 l/O/A(molra.t1o) 442011 43:5 1 50:5:1 30:2:1 50:2 1 64:2:1 Temperature, O 10 8 8 6 8 8 Time, minutes 30 21 18 27 22 27 Benzene converted, mol percent None 99 96 98 95 88 p-d -t-Bntylbenzene, mol percent (rec.) None 34 58 34 p-di-t-Butylbenzene, mol percent (IR) None 19 38 7O =90% acid from alkylation of isobutane and butenes.

(Red) Recovered by crystallization from liquid product, based on benzene charged.

(IR) Yield by infrared analysis, based on benzene charged.

TABLE II Results using toluene a Pentene-2 Hexene-2 Hexone-2 4-rnethyl- 4-methyl- 4-methyl- Hexene-2 pentene-2 pentene-2 pentene-2 H2804 conc. 90 98 90 I/O/A(molrat10) 15:0.9 1 15:1:1 40:0.9 1 51:0.9 1 60:0.9:1 78:1:1 42:0.9 1 Temperature, C... 30 10 30 10 10 6 30 Time, minutes 30 26 29 26 30 27 Toluene converted, mol percent 94 93 99 96 92 98 91 p-t-Alkyltoluene (IR), mol percent.-- 6 15 15 73 34 51 31 m-t-Alkyltoluene (IR), m01percent Trace Trace Trace Trace 1 Trace 30 Isobutane charged in all tests except 15. Isopentane charged.

90% acid from alkylation of isobutene and butenes. IBF;.H2O (75% BFg).

(IR) Yield by infrared analysis, based on theoretical.

meta t-alkyltoluene. Tests 10-12 and No. 16 were carried out using an n-olefin as the hydrogen acceptor. Tests 4 l1 and 12 show that a shift of temperature from 10 C. to 30 C. had no efiect on the amount of t-butyltoluene produced or on the distribution between the para and meta isomers. Test No. 16, which was carried out at about the conditions of test No. 12, except that BFs hydrate was used as the catalyst, shows not only a-larger yield of the t-butyltoluene, but a very great amount of isomerization of the t-butyltoluene; t-butyltoluene consisted of almost equal amounts of the meta and the para isomers, which is remarkably dificrent from the results using sulfuric acid.

Test No. 13 shows that a very remarkable increase in yield of t-butyltoluene is obtained without increase in meta isomer production, when a branched chain 6 carbon atom olefin is used as the hydrogen acceptor. The increase in yield over the corresponding 6 carbon atom n-olefin is of fivefold.

Test No. 14 was carried out under conditions similar to those of test No. 13 except that 98% acid was used as the catalyst. This test shows that toluene responds to higher acid concentration in a manner similar to benzene and the yield of t-butyltoluene is markedly decreased.

Test No. 15 utilized isopentane as the isoparaflin. This test shows that it is possible to obtain high yield of parat-pcntyltoluene by use of this process.

The comparative results set out in Tables I and II clearly show that a very large improvement in yield of the desired tertiary alkylbenzene is obtained when a branched chain olefin is utilized as the hydrogen acceptor instead of utilizing an n-olefin as the hydrogen acceptor. Further, these tests show that by the use of sulfuric acid catalyst, it is possible to obtain essentially pure para-dit-alkylbenzene or para-t-alkyltoluene as the alkylate product.

Thus having described the invention what is claimed is:

1. A process which comprises (A) contacting (I) (a) isobutane, (b) an aromatic hydrocarbon selected from the class consisting of benzene and toluene, and (c) a branched chain olefin containing from 5 to 8 carbon atoms, in a molar ratio of isobutane to aromatic hydrocarbon of between about 38 and 78, and in a molar ratio of said olefin to benzene of essentially 2 and of said olefin to toluene of essentially 1, with (II) sulfuric acid catalyst having a concentration between about 88% and 92%, in a volume ratio of acid to hydrocarbon charged of between about 1 and about 1.5, at a temperature between about 5 C. and about 10 C., for a time between about 20 and 40 minutes, (B) separating hydrocarbons from acid and (C) recovering from said hydrocarbons parafiin derived from said olefin and, as essentially the only t-butylated benzene present, p-di-t-butylbenzenc, in the case of benzene charged, and p-t-butyltoluene, in the case of toluene charged.

2. The process of claim 1 wherein said aromatic hydrocarbon is benzene.

3. The process of claim 1 wherein said aromatic hydrocarbon is toluene.

4. The process of claim 1 wherein said olefin is 2- methylbutene-Z.

5. The process of claim 1 wherein said olefin is 2,3,4- trimethylpentene-Z.

6. The process of claim 1 wherein said olefin is 2- methylpentene-Z.

References Cited in the file of this patent UNITED STATES PATENTS 2,653,980 Condon Sept. 29, 1953 2,681,362 Kennedy et a1. June 15, 1954 2,712,033 Schenider June 28, 1955 

1. A PROCESS WHICH COMPRISES (A) CONTACTING (I) (A) ISOBUTANE, (B) AN AROMATIC HYDROCARBON SELECTED FROM THE CLASS CONSISTING OF BENZENE AND TOLUENE, AND (C) A BRANCHED CHAIN OLEFIN CONTAINING FROM 5 TO 8 CARBON ATOMS, IN A MOLAR RATIO OF ISOBUTANE TO AROMATIC HYDROCARBON OF BETWEEN ABOUT 38 AND 78, AND IN A MOLAR RATIO OF SAID OLEFIN TO BENZENE OF ESSENTIALLY 2 AND OF SAID OLEFIN TO TOLUENE OF ESSENTIALLY 1, WITH (II) SULFURINC ACID CATALYST HAVING A CONCENTRATION BETWEEN ABOUT 88% AND 92%, IN A VOLUME RATIO OF ACID TO HYDROCARBON CHARGED OF BETWEEN ABOUT 1 AND ABOUT 1.5, AT A TEMPERATURE BETWEEN ABOUT 5* C. AND ABOUT 10* C., FOR A TIME BETWEEN ABOUT 20 AND 40 MINUTES, (B) SEPARATING HYDROCARBONS FROM ACID AND (C) RECOVERING FROM SAID HYDROCARBONS PARAFFIN DERIVED FROM SAID OLEFIN AND, AS ESSENTIALLY THE ONLY T-BUTYLATED BENZENE PRESENT, P-DI-T-BUTYLBENZENE, IN THE CASE OF BENZENE CHARGED, AND P-T-BUTYLTOLUENE, IN THE CASE OF TOLUENE CHARGED. 